1. Field of the Invention
The present invention relates to an image data transfer system operable with an electronic still camera and, more particularly, to an image data transfer system feasible for the transfer of image data generated an electronic still camera to a personal computer or similar equipment connected thereto.
2. Description of the Background Art
An image data transfer system is conventional in which image data representative of an image picked up by a digital electronic still camera or similar image pick-up device are sent to desired equipment connected to the camera. For example, Japanese patent laid-open publication No. 83666/1993 teaches a system for recording and reproducing images picked up. Japanese patent application No. 101740/1994 discloses an electronic still camera, and a method of sending image data generated thereby.
In the above image recording and reproducing system, when a camera shoots a desired subject, an image representative of the subject is incident on a CCD (Charge Coupled Device) image sensor or similar imaging device via a lens. In response, the imaging device generates image signals in the form of YC signals consisting of a luminance signal y and chrominance signals C. The image signals or YC signals are sent as analog or digital image data from the camera to DAT (Digital Audio Tape) or similar recording and reproducing equipment connected to the camera. In the equipment connected to the camera, the image data are written to a digital audio tape and then read thereoutof to be reproduced on, e.g., a display. The camera and DAT equipment are connected to each other by an exclusive transfer cable. The camera sends the image data to the DAT equipment over the cable in response to synchronizing pulses generated by a timing signal generator which is built in the camera.
In the prior art electronic still camera and image data transfer method mentioned previously, image signals representative of a subject picked up by a CCD image sensor or similar imaging device are transformed to digital YC signals, compressed by a preselected compression scheme, and then recorded in a semiconductor memory, e.g., a memory card removably mounted to the camera. The compressed image data are read out of the memory card and then sent to a computer system via serial communication interfaces respectively included in the camera and computer system. The interfaces are based on, e.g., RS-232C or RS-422 as prescribed by EIA (Electronic Industries Association) standards. A printer or similar peripheral is connected to the computer system. The RS-232C or RS-422 interfaces are connected to each other by a cable including a data line assigned to the image data, and a control line assigned to a control signal which is selectively controlled to an ON state or to an OFF state. For example, when the control signal being sent from the computer system to the camera is in an ON state, image data are transferred from the camera to the computer system over the data line. The data transfer from the camera is interrupted when the control signal goes OFF, and then resumed when it again goes ON. On receiving the compressed image data, the computer system expands them, and displays the expanded image data or prints them out.
However, in both of the above conventional systems, the camera is operable only with a particular kind of equipment, and therefore knows the transfer rate available with the equipment before the connection of the equipment. Particularly, the former system does not include RS-232C or similar communication interfaces having a variable transfer rate, so that the image data must be transferred only at a transfer rate particular to the camera. The latter system including the RS-232C or similar communication interfaces is capable of varying the transfer rate within a certain range. However, even the latter system has a drawback that a particular transfer rate matching a processing speed available with the computer must be set on, e.g., a dip switch beforehand.
Generally, not only the exclusive equipment but also a general-purpose personal computer is capable of receiving the image data. However, when a personal computer receives serial data, the transfer rate depends on the hardware characteristic of the computer. Of course, if the communication between the image pick-up device and the computer is bidirectional, they can interchange information in order to set up a compatible transfer rate. However, an electronic still camera or similar miniature apparatus has only a limited number of pins on its connector and only a limited drive circuit scale. Hence, an additional data line is not desirable with this kind of apparatus. In this condition, the sending station must be matched in transfer rate to the receiving station.